1. Field of the Invention
This invention relates to a laminograph and an inspection and repair device using the same. More particularly, this invention relates to a laminograph for detecting X-rays passed through a subject to obtain a tomographic image of the subject, which is used for, for example, nondestructive testing of the interior of multi-printed boards or the soldered parts of the surface mounted boards. This invention further relates to an inspection and repair device to inspect and repair the subject using the laminograph.
2. Description of the Related Art
This type of laminograph has recently attracted attention as being capable of use in the examination of the soldering to be boards of flipchip mounting or surface mounting fitted with J lead terminals, bump fitted passive chip parts and other parts whose connections cannot be examined from the upper surface. It is basically the same as the tomography device widely used in medicine which. obtains a radiographic image along one plane using X-ray film. Whereas in this kind of laminography, the plane sensor output in digitally processed to produce a tomographic image by image processing.
FIG. 52 shows a laminograph of the prior art as described in Japan Patent Disclosure (Kohyou) Hei 2-501411. In this figure, the focal point is moved in a circular scan by a focal point scanning X-ray tube 91. A rotating X-ray detector 94, which is a two-dimensional plane sensor, rotates in synchronization with the focal point and the multiple radiographic images obtained from X-rays passing through a subject 92, which have been collected during this rotation, are added by digital processing to form a single tomographic image. The tomographic image is an image which follows a single focal plane 93 decided by the rotational radius of the focal point and the rotational radius of the rotating detector 94.
FIG. 53 shows a laminograph of the prior art as described in Japan Patent Disclosure (Kokai) Hei 6-88790. In the laminograph shown in this figure, a conical X-ray beam 102 generated from an X-ray tube 101 is measured by an X-ray I.I. (X-ray Image Intensifier) 104 which is a two-dimensional X-ray plane sensor. A subject 103 is penetrated by these X-rays along the measurement plane, and it is possible to produce a tomographic image which precisely fits a single focal plane 105 by image displacement and addition-processing of the multiple radiographic images thus obtained. The focal plane can be changed if the process is repeated with the displacement altered.
In the laminographs of the prior art described above, tomographic images are prepared repeatedly by displacing the position at which the subject is set or by changing the displacement when addition-processing is performed in order to align it precisely along the desired plane, and the optimal focal position is thus obtained. However, when the thickness of the board to be examined varies or when it is curved, it is necessary to focus as described above for each board. This makes the procedures necessary for a laminograph of the prior art complex and time-consuming, which is a problem.
Non-destructive inspection methods in which the subject is irradiated and the X-rays which have passed through the subject are examined already exist. But it may be impossible to assess the faults and structures from such images from transmitted X-rays depending on the kinds or structures of the subjects, and laminography is used in such cases.
FIG. 54 shows the structure and operation of such a laminograph. In this laminograph, multiple line sensors 397 in an array receive each radiographic image in each direction, and the tomographic image is obtained by shifting these so that the desired images overlap among different direction images and by overlapping radiographic images thus shifted.
In greater detail, in the laminograph shown in FIG. 54, there is an X-ray tube 391, which is a penetrating radiation source, multiple line sensors 397 opposite this, which are arranged in equally spaced n lines and detect this radiation on their lines through their spatial resolution. Between this X-ray tube 391 and line sensors 397, there is a transport mechanism 395 which is moved in parallel and at right angles to the direction of the resolution of the line sensors 397, and a subject 393 is placed on this. It also has a signal collection part 390 which collects transmission signals from each of line sensors 397, an addition and averaging part 392 which shifts, adds and averages the radiographic images received from the different line sensors 397, while they are displaced the position of the parallel movement, and a CRT 394 for image display. In FIG. 54, 398 is an X-ray control part and 396 is a mechanism control part.
In the laminograph thus structured, a tomographic image of the required layer section of the subject 393 is obtained by shifting, adding and averaging the radiographic images which are obtained from each of line sensors 397 by sampling the transmission signals at every displacement .DELTA.P, as subject 393 moves, which shifting amount .DELTA.S is determined according to the distance to the required layer section from the focal point of X-ray tube 391.
It is necessary to carry out the inspection using an enlarged radiographic image in order to improve the resolution in the inspection of electronic parts such as PWBs. In the case of using the laminograph this may be a partially enlarged laminogram. In case of inspecting the subject with a large area, such as a PWB, some of the parts mounted on the subject are enlarged and inspected, which makes an overall assessment difficult. It is also necessary to repair the faulty part, but it is difficult to transmit the inspection results to the repair line. Previously, a hard copy of the image or notes of handwriting have been used. For important cases, it is necessary to keep the documents of the inspection results for many years but storage is not easy.